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Newton's Laws of Motion - Part I |
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We have seen that a body moves under the influence of force. If the force applied is removed, the body will come to rest. Also, you may have noticed that it is difficult to start a body in motion. There is some amount of resistance in the beginning, but once the body picks up motion, the resistance disappears. For example, the first gear in the car is the most powerful one, as it has to drag the stationary engine and car from a halt position. Everyday phenomena like these are explained in Newtonís Laws of Motion. What
we will study in this chapter
: 1. Newtonís first law of Motion
If you push a marble on a smooth surface such a dining table, you
will see that the marble ìlikesî to continue to move in a straight line.
If instead of a marble, you take a book, you will see that the book is
resisting to be moved. For many years many scientists thought as to why objects
behave the way they do to applied forces. Newton put these ideas very neatly
in his first law of motion. Newtonís
first law of motion states that every object continues in its state of rest or
of uniform motion in a straight line unless acted upon by an external unbalanced
force. In
the examples of marble and book, both will ìlikeî to stay in their
initial state of rest. In case of marble, because the mass is small, its
resistance to change in its state of rest is not felt by us. While in the
case of the book, we sure do feel the resistance. Once the marble is in
motion, it will continue to move in a straight line. It comes to a stop
because of friction between its surface and the table. If the friction did
not exist, the marble would continue to go in a straight line eternally!! If
you want to stop the moving marble, you will have to use a bit of force. So
unless and until an external ìunbalancedî force is applied, the marble
will not stop. The word unbalanced is important because if the forces were
balanced they would have no effect on the motion of the object. The term
uniform motion is also important. Uniform motion is a continuous motion in a
straight line. Motion along the circumference of a circle (where the
direction is changing at every point), an extra force is acting at every
point and the motion is said to be non-uniform. Newtonís
first law of motion gives us a definition of force.
Force is that physical quantity that tends to change the state of rest or
uniform motion of a body. Or the force can be defined as the influence that
tends to change the speed and direction of a stationary or a moving body.
Force is a vector quantity.
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